Temperature Rise of the Post & on the Root Surface During Ultrasonic Post Removal

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Temperature rise of the post and on the root surface

during ultrasonic post removal

J. C. Budd, D. Gekelman & J. M. White

Department of Preventive and Restorative Dental Sciences, School of Dentistry, University of California, San Francisco, CA, USA

Abstract

Budd JC, Gekelman D, White JM. Temperature rise of the

post and on the root surface during ultrasonic post removal.

International Endodontic Journal, 38, 705711, 2005.

Aim To determine the temperature rise on the root

surface caused by ultrasonic post removal using

different devices and techniques in a laboratory setting.

Methodology Two ultrasonic devices, one piezo-

electrical (Pi) and one magnetostrictive (Ma), were

investigated. A serrated titanium post was placed into

the distal root canal of a human mandibular first molar.

Four coolant parameters were utilized: no air, no water,

no evacuation (NN), air only with high-speed evacu-

ation (A), 15 mL min)1 water coolant with high-speed

evacuation (W15) and30 mL min)1 water coolant with

high-speed evacuation (W30). Five simulated post

removals were measured at two locations, the post (P)

and the root (R), for each coolant parameter. Tempera-

ture rise was measured at 30, 60, 90and 120 s intervals

using calibrated infrared thermography (n 80). Tem-

peratures were recorded at 45 ms intervals. Data were

analysed using repeated measures anova with the

Scheffe post hoc test (P 0.05).

Results The overall mean pooled effect showed

that temperature rise for P 20.1 27.9 C and

R 10.9 7.9 C were significantly different. Signifi-

cant differences in temperature rise were: Pi > Ma,

P > R, NN > A W15 W30 however, A > W30.

Conclusions There were significant differences in

temperature rise as a function of ultrasonic device,

location on the tooth and cooling method utilized for

post removal.

Keywords: post removal, root, temperature, ultra-

sound.

Received 17 August 2004; accepted 16 May 2005

Introduction

Ultrasonic devices might be used for intraradicular post

removal. Clinicians utilize a range of techniques,

including no coolant, to improve visibility and air/

water coolant to remove debris (Cohen & Burns 2001).

One concern with these devices is the heat that they

generate, which could penetrate into periradicular

tissues and cause damage (Atrizadeh et al. 1971).

The ultrasonic energy utilized in endodontic devices

is generated by one of two types of ultrasonic

transducers that convert one form of energy into

another. Piezoelectrical (Pi) transducers produce ultra-

sonic energy by transforming electricity into ultrasonic

vibrations. Crystals within the transducer (usually

made of quartz) are vibrated by the electricity flowing

through them. By applying an alternating electrical

field across the crystals, the quartz is compressed and

released producing vibration of the tip. Magnetostric-

tive (Ma) transducers use ferromagnetic materials and

certain nonmetals called ferrites. A change in dimen-

sion occurs when a rod or bar of this material is

subjected to an alternating magnetic field producing

vibration of the tip. Pi and Ma devices also produce

noise and heat.

Research has focused on the efficiency of different

ultrasonic devices by measuring the time and force

required to achieve post removal. Dixon et al. (2002)

compared the time required to remove a 16 mm No. 5

(0.050 in) Para-post cemented with zinc phosphate

Correspondence: Joel M. White, DDS, MS, Professor, Division of

Biomaterials and Bioengineering, Department of Preventive

and Restorative Dental Sciences, 707 Parnassus Avenue

Box 0758, San Francisco, CA 9414-0758, USA (Tel.: +1 415

476 0918; fax: +1 415 476 0858; e-mail: whitej@

dentistry.ucsf.edu).

2005 International Endodontic Journal International Endodontic Journal, 38, 705711, 2005 705


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cement using the Piezo-Ultrasonic (Spartan USA,

Fenton, MO, USA) and the Enac OE-50 (Osada Inc.,

Los Angeles, CA, USA) at their highest intensities. The

results showed that both devices were effective with

typical post removal times of


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was removed at the level of the cemento-enamel

junction. The removal of the crown also eliminated

the possibility of heat dissipating into the crown.

Temperature rise was measured at two locations.

The first location was at the coronal aspect of the post

root interface (P). The second location was at the distal

root surface 3 mm from the apex of the root (R) at the

terminus of the post (Fig. 1). The ultrasonic tip supplied

with each device was applied to the post at the junction

of the post and tooth surface for a duration of 120 s

using a circumferential technique around the post. The

force applied to the toothpost interface was designedto simulate the range of force used clinically during

post removal.

The experimental setup with evacuation and ultra-

sonic tip is illustrated in Fig. 1. The tooth was held

stationary by clamping the mesial root. Temperatures

were measured using an infrared camera (Model

TH-5104; Mikron Infrared Inc., Oakland, NJ, USA).

The camera measures temperatures by performing a

scan of the field of focus every 45 ms. The accuracy of

the camera was verified to within 0.5 C using heated

water at 51 C and cooled water at 19 C. The infrared

camera has a mercurycadmiumtellurium linear

array detector which enables the camera to detect

changes in temperature. The operator distinguished

changes in temperature using two different methods.

First, the camera was programmed to distinguish

variations in temperature by producing a different

coloured image on the monitor for every 5 C change

in temperature. Secondly, numeric point values to one

significant digit were displayed on the screen in C.

A measurement of room temperature was simulta-

neously recorded as a baseline for temperature rise. An

example of an image produced by the camera is

provided in Fig. 2.

Following each trial, the videotape was used to

record temperatures at 30, 60, 90 and 120-s intervals.

Five repetitions were recorded for each location for

each cooling regimen (n 80). Five repetitions were

chosen based on a sample size calculation using

repeated measures analysis of variance (anova) design

with power 0.8, minimum detectable difference of

5 C and SD of residuals of five for the eight treatmentgroups over the four time points measured. The

temperature rise was calculated by taking the maxi-

mum temperature at each interval and subtracting the

baseline room temperature. The temperature of the

toothpost system was allowed to return to room

temperature in between repetitions. All data were

obtained and recorded by a single operator. Independ-

ent variables were as follows: device type, location on

the tooth and cooling regimen. The dependent variable

was temperature rise. Results were analysed for statis-

tical significance using repeated measures anova with

the Scheffe post hoc test (P 0.05).

Results

The overall mean pooled effect for temperature rise

following instrumentation with each ultrasonic device

is displayed in Table 2. Temperature rises were higher

for the Pi, especially with no air and no water coolant.

Figure 1 Experimental setup showing the ultrasonic hand-

piece, high volume evacuation (E), the lens of the infrared

camera (L) and the tooth with post. Temperature measure-

ments were taken at the posttooth interface (P) and at the

apical root surface (R).

+22.6

59.124.55

25.731.0

+

(200.0)50.0

45.0

40.0

35.0

30.0

25.020.0

15.0

10.0< (10.0)

P 0

+

++

Figure 2 Infrared camera image showing temperature scale

on the right, a baseline temperature of 22.6 C with a

temperature of 59.1 C at the toothpost interface and 31 C

at the surface of the root during piezoelectric post removal

with coolant parameter air only (treatment condition A).

Budd et al. Temperature from post removal



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Table 3 shows the temperature rise as a function of

device type and distinguishes between the locations on

the tooth. As expected, the temperature at the post

tooth interface was higher than at the surface of the

root. The posttooth interface and root surface heat

profiles were uniform and followed the outline of the

tooth and we did not visualize any change in heat

profile at the slight concavity of the mesial aspect of the

distal root used in the study. Figures 3 and 4 show

temperature rise as a function of device, location and

cooling regimen. Temperature rise was inversely pro-

portional to air and water coolant. Statistically signi-

ficant differences were found for temperature rise at

the post location using the Pi device where

NN > A W15 W30. There were no statistically

significant differences in temperature rise at the post

location using the Ma device where NN A W15 W30. At the root, results for the Pi device were

NN > A W15 W30. At the root, results for the

Ma device were NN A W15 > W30. The mean

pooled results were significantly different between

device type (Pi > Ma) and location on the tooth

(P > R). Statistical significance regarding temperature

rise between cooling regimens was as follows: NN > A,

A W15, W15 W30 and A > W30 for both

devices tested. Temperature rise as a function of time

and location is listed in Table 4. Overall, the majority of

the temperature rise at the post occurred within the

first 30 s whereas the temperature rise at the root

surface continued to rise up to 90 s.

Discussion

The ultrasonic devices used in this study were selected

to compare the differences in the temperature rise using

different ultrasonic transducers. The four cooling reg-

imens used in this study were selected to include

common cooling techniques currently used by many

practitioners. The NN parameter was selected as this

technique provides the best visualization for the clini-

cian, although with the highest temperature rise.

Temperature rise at both the crown and the root was

measured in order to determine the amount of heat

conducted down the post to the root. The distal root of

the mandibular molar was chosen as this represents a

common site of post placement. The temperature rise at

the distal surface of the root was measured to facilitate

imaging with the infrared camera. The 120 s duration

of instrumentation was chosen to simulate a clinical

setting in which the progress of post removal would be

Table 3 Temperature rise as a function of ultrasonic deviceand location

Device/location Temperature rise (C) 1 SD

Piezoelectric/post 27.9 34.2

Piezoelectric/root 12.3 16.6

Magnetostrictive/post 1 3.9 8.9

Magnetostrictive/root 7.9 5.3

NN A W15 W30 NN A W15 W300

10

20

30

40

50

60

70

80

90

100

110

Temprise(C)

Piezoelectrical Magnetostrictive

Figure 3 Temperature rise at the post as a function of

ultrasonic device and cooling regimen.

Table 4 Mean temperature rise (C) as a function of location

and time interval

30 s 60 s 90 s 120 s

P os t 23.8 31.0 29.6 35.8 31.0 36.5 27.1 35.3

Root 6.7 7 .8 12.0 15.3 14.8 1 8.9 15 .6 20.9

Table 2 Temperature rise as a function of ultrasonic device

Device Temperature rise (C) 1 SD

Piezoelectric 20.1 27.9

Magnetostrictive 10.9 7.9

NN A W15 W30 NN A W15 W30

0

10

20

30

40

50

60

70

80

90

100

110

Temprise(C)

Piezoelectrical Magnetostrictive

Figure 4 Temperature rise at the root as a function of

ultrasonic device and cooling regimen.

Temperature from post removal Budd et al.

International Endodontic Journal, 38, 705711, 2005 2005 International Endodontic Journal708


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verified periodically and some form of coolant and

evacuation applied to wash the area.

Heat is produced from ultrasonic devices through

three different mechanisms. First, via friction created

between the titanium post and the ultrasonic tip.

Secondly, via the temperature of the coolant flowing

through the handpiece. Thirdly, via acoustic energyabsorption of ultrasound transmitted to the tooth

(Bergeron et al. 2001).

The Pi transducer caused a significantly greater

temperature rise than the Ma transducer when the NN

cooling regimen was used. However, the Ma device

produced a higher temperature using the W15 and

W30 parameters at both the crown and the root than

the Pi device. Although the posttooth system was

allowed to cool to room temperature between repeti-

tions, the heat produced and retained within the

transducer most likely explains the above observation

caused by the water coolant flowing through the

handpiece. The increased temperature of the water

coolant caused by the ferromagnetic rods might have

contributed to the increased temperatures observed

with the use of the Ma device.

Repeated measure methods were used reducing the

sample size estimate to five repetitions per treatment

condition. This allowed for the determination of statis-

tical differences between the two devices and four

coolant regimens over time at the post and root surface.

One post and root was utilized in order to limit the

variability because of differences in remaining dentine

thickness and root volume. By this method, it was

possible to determine differences in heat produced as afunction of the devices and cooling regimen. The

average length of the distal root of a lower first molar

is 14 mm. In the cervical region, the mesial/distal

width is generally equal to the buccal/lingual width,

9 mm (Ash 1993). By comparison, the average root

length for maxillary and mandibular canines is 16 mm

with cervical mesial/distal width of 5.5 mm and

cervical buccal/lingual diameter of 7 mm (Ash 1993).

Anterior teeth with less root volume would be expected

to have higher temperature rises than those that we

reported and roots with larger volumes would be

expected to have lower rises than those we reported.

Further studies using different size roots would define

the range of temperature rises that might be expected

for all teeth. However, the sample size would be very

large for each treatment group accounting for variation

in root size, remaining dentine thickness and volume. A

change in heat profile at the slight mesial concavity of

the mesial aspect of the molar was expected but did not

occur. The infrared images confirmed the majority of

the heat diffused down through the post and into the

dentine heating the root surface uniformly. It can be

hypothesized that within the range of remaining

dentine of the root (12 mm) that the temperature

effects from the diffused heat were within 5 C because

no difference was visualized in the infrared thermalprofile. The application of the ultrasonic device was

limited to the post for 2 min to simulate a clinical

application. Generally, clinicians use a device for this

amount of time and then stop to inspect the area. Even

2 min was also a good time as the temperature rise

reached steady state within 90 s and did not continue

to increase.

Results from Eriksson & Albrektsson (1983) sug-

gested that a temperature rise above 10 C can cause

irreversible damage to the periodontal ligament and

bone. Comparisons of temperature rise between cooling

regimens were made to determine what regimen cooled

the tooth sufficiently to consistently remain below the

10 C threshold. The infrared camera used to measure

temperature rise in this study allowed the measure-

ment of temperature rise to be recorded over a broad

area and to a degree of accuracy that is not achievable

with the traditional thermocouples used in previous

studies. Thermocouples allow temperatures to be

recorded at only those locations between the thermo-

couples where a circuit can be created. In contrast, an

infrared camera allows temperatures to be recorded at a

number of locations simultaneously with accuracy to

one significant digit. Using infrared thermography, the

area of highest temperature rise can be pinpointed andmeasured (McCullagh et al. 2002). Thermocouple

accuracy can be negatively affected by a number of

factors including how the thermocouple adheres to the

material to be measured, alteration of the electrical

circuit and specific operating temperature ranges rela-

ted to thermocouple types. All of these factors are

eliminated with the use of an infrared camera.

Recently, Satterthwaite et al. (2003) reported tem-

perature changes from ultrasonic vibration of ceramic

and stainless steel posts. The results of their study

indicated temperature rises lower than those in the

present report. Their study utilized morphologically

similar canine teeth mounted in a mounting jig

(silicone rubber) that would have increased the vari-

ability of the measurements and also reduced the

temperature rise as compared with the present study.

In their study, k-type thermocouples were mounted on

the root surface, whereas infrared thermography was

utilized in the present study. Satterthwaite et al. (2003)




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did not report the amount of water coolant and they

used longer time intervals, up to 30 min, for post

removal. The differences in the results of these studies

are most likely because of differences in experimental

technique and materials. Both utilized the tip of the

ultrasonic device in contact with the post, creating heat

by friction and both studies suggest temperature riseslikely to cause adverse thermal effects to adjacent

tissues. In the present study, the majority of tempera-

ture rise occurred at the posttooth interface within the

first 30 s. The temperature rise continued to increase at

the root surface up to 90 s before reaching a steady

state. The difference in time to reach steady state at the

crown and root surface is presumably because of the

diffusion of heat through the tooth taking time to reach

the root surface.

In summary, this study shows that failure to provide

some form of water coolant during ultrasonic post

removal can result in temperature rises that exceed the

10 C threshold. The results of the present study also

illustrate the need of using the minimum time to reach

the treatment objective; even 15 mL min)1 water

coolant can permit a temperature rise that exceeds the

10 C threshold. In this study, the temperature rise

never exceeded the 10 C threshold when using

30 mL min)1 water coolant. The results showed no

statistical significance between 15 and 30 mL min)1

water coolant. Nevertheless, we recommend that a

minimum of 30 mL min)1 water coolant be used during

ultrasonic post removal procedures as this regimen did

not exceed the defined temperature rise threshold.

Future studies should focus on determining differ-ences in temperature rise comparing different teeth,

varying dentine and enamel thicknesses, a range of

clinical techniques including a range of applied force

and different coolant conditions. The intensity of the

temperature rise, the frequency of the thermal insult,

the size of the thermal mass and the duration of

temperature rise are all important factors to be consid-

ered in determining adverse thermal effects to tissue. In

a clinical setting it would be expected that the

temperatures would be lower given the larger body

mass for heat dissipation and blood flow of surrounding

tissues. These factors are likely to have an impact in

reducing the amount of heat that is actually absorbed

by periodontal tissues.

Acknowledgements

We would like to thank Kim Tran, SRA, for laboratory

assistance, data management and graphics. We also

thank Steve Barrabee, J.D. at Bradley, Curley, Asiano,

Barrabee and Crawford, P.C. for collaboration on the

design of this study and fruitful discussions on the

results. This work supported in part by a grant from

The Dentists Insurance Company of California.

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Temperature Rise of the Post & on the Root Surface During Ultrasonic Post Removal

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